The present invention has been specifically invented to improve the control of dispensing draught beer in commercial establishments. However, other applications are possible including medical and any fluid or gas system which requires a linear or any predetermined relationship between temperature variations and pressure output.
In commercial establishments including bars and restaurants it is customary to store beer kegs inside walk-in cold storage refrigerators. These walk-in cold storage refrigerators can store many beer kegs of various brands. Pressurized CO.sub.2 is used to pump the draught beer from the keg to the bar.
Draught beer contains CO.sub.2 in solution. The two most common elements that affect CO.sub.2 levels in draught beer are elevation and temperature. If too much CO.sub.2 escapes from the draught beer during the pumping to the bar, then excessive foam is created, and the beer loses carbonation and becomes flat tasting. FIG. 1 shows one typical temperature and elevation compensation chart for one type of draught beer. The idea is to maintain the CO.sub.2 solution in the beer during pumping regardless of temperature variations in the cold storage refrigerator. CO.sub.2 pressures in draught beer range between 11 psi and 26 psi depending on the brewer. The problem as yet unsolved in the art is how to properly compensate for temperature fluctuations caused by opening the door and from moving food stuffs at various temperatures in and out of the cold storage refrigerator.
FIG. 2 shows a layout of a walk-in refrigerator having a hypothetical computer controlled temperature compensated pressure regulating system. It is not economically feasible to install this system in a cold storage room. However, it is helpful to describe the functioning of the present invention by starting with a computer system model. This computer system computes the air temperature in the cold storage refrigerator and calculates the duration of time of any deviations from the norm. Then an algorithm is executed which simulates the temperature change of the beer (in nominally one half keg) during the measured temperature and time deviation of the ambient air in the cold storage refrigerator. Finally, a new pressure is calculated per the table in FIG. 1, and a new pressure is set on the pressure regulating valve to the keg. This computerized method of pressure compensation is too expensive since it requires a computer control loop.
Another known solution is to insert a temperature sensor directly into the keg. This method is also very expensive since it requires an approved probe in contact with publicly consumed beverages. It also requires bacteria and leak proof seals into the keg.
The present invention provides the same efficiency as the computer control loop noted above. However, the result is accomplished with an inexpensive temperature compensated pressure regulator valve. The basic principle uses a common pressure regulator valve having a temperature compensating adapter. The adapter has a closed compartment which encases an expandable fluid such as wax. When the wax expands during a rise in the ambient air temperature, it forces a piston down into the pressure regulator, thereby altering the spring tension in the regulator and increasing the output pressure. The closed compartment size, the thermal mass of the wax and the spring tension in the common regulator are designed to linearly compensate for a given volume of beer (nominally half a keg) over a set temperature range (30.degree.-40.degree. F.). The relationships described in FIG. 1 are maintained.
Thus, the control results of a costly computer system are duplicated in an inexpensive mechanical pressure regulator.